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id="content-inner"><div id="post"><article class="post-content" id="article-container"><h2 id="NSTimer叫做“定时器”，它的作用如下"><a href="#NSTimer叫做“定时器”，它的作用如下" class="headerlink" title="NSTimer叫做“定时器”，它的作用如下"></a>NSTimer叫做“定时器”，它的作用如下</h2><blockquote>
<ul>
<li>在指定的时间执行指定的任务</li>
<li>每隔一段时间执行指定的任务</li>
<li>NSTimer只有被加入到runloop, 才会生效, 即NSTimer才会被真正执行</li>
</ul>
</blockquote>
<hr>
<h4 id="常用属性"><a href="#常用属性" class="headerlink" title="常用属性"></a>常用属性</h4><figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">@property</span> (<span class="keyword">copy</span>) <span class="built_in">NSDate</span> *fireDate;	<span class="comment">//重新设置定时器开始运行的时间</span></span><br><span class="line"><span class="keyword">@property</span>(<span class="keyword">readonly</span>, <span class="keyword">getter</span>=isValid) <span class="type">BOOL</span> valid;  <span class="comment">// 定时器是否正在运行中</span></span><br></pre></td></tr></table></figure>



<h4 id="常用方法"><a href="#常用方法" class="headerlink" title="常用方法"></a>常用方法</h4><ul>
<li>创建NSTimer</li>
</ul>
<figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">//每隔ti秒，调用一次aTarget的aSelector方法，yesOrNo决定了是否重复执行这个任务</span><br><span class="line">//该定时器schedules on the current run loop in the default mode：scheduledTimerWithTimeInterval相比它的小伙伴们不仅仅是创建了NSTimer对象, 还把该对象加入到了当前的runloop中</span><br><span class="line">- (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo; </span><br><span class="line">// 该方式默认会将定时器添加到NSRunLoop中(常用⭐️⭐️⭐️⭐️⭐️)</span><br><span class="line">+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo; </span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line">//需要指定runloop的 - (void)addTimer:(NSTimer *)aTimer forMode:(NSString *)mode</span><br><span class="line">// 该方式必须手动加入到当前循环中去，必须显式加入：[[NSRunLoop currentRunLoop] addTimer:_timer forMode:NSDefaultRunLoopMode];	</span><br><span class="line">+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;	</span><br><span class="line">//包含启动时间的定时器</span><br><span class="line">- (instancetype)initWithFireDate:(NSDate *)date interval:(NSTimeInterval)ti target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats;</span><br></pre></td></tr></table></figure>

<ul>
<li>销毁NSTimer</li>
</ul>
<figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="comment">// 创建一个定时器如果不手动触发定时器，那么定时器会过TimeInterval秒后自动执行selector</span></span><br><span class="line"><span class="comment">// 如果想立刻执行直接调用fire方法													</span></span><br><span class="line"><span class="comment">// 在重复执行的定时器中调用此方法后立即触发该定时器，但不会中断其之前的执行计划；</span></span><br><span class="line"><span class="comment">// 在不重复执行的定时器中调用此方法，立即触发后，就会使这个定时器失效。</span></span><br><span class="line">- (<span class="type">void</span>)fire;			 			<span class="comment">// 立刻启动	:</span></span><br><span class="line">- (<span class="type">void</span>)invalidate;			<span class="comment">// 停止定时器(永久停止)不是暂停定时器, 这个是唯一一个可以将计时器从runloop中移出的方法：stop a repeating timer and remove timer from RunLoop</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>



<hr>
<h5 id="基本使用"><a href="#基本使用" class="headerlink" title="基本使用"></a>基本使用</h5><figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//不重复，只调用一次。timer运行一次就会自动停止运行 </span></span><br><span class="line"><span class="keyword">self</span>.myTimer = [<span class="built_in">NSTimer</span> scheduledTimerWithTimeInterval:<span class="number">1.5</span> target:<span class="keyword">self</span> selector:<span class="keyword">@selector</span>(scrollTimer) userInfo:<span class="literal">nil</span> repeats:<span class="literal">NO</span>];  </span><br><span class="line"></span><br><span class="line"><span class="comment">//方式1：创建一个定时,该方式默认会将定时器添加到NSRunLoop</span></span><br><span class="line"><span class="comment">//需要重复调用， repeats参数改为 YES . ---&gt; 定时器的模式是默认的</span></span><br><span class="line"><span class="comment">//每1秒运行一次function方法。  </span></span><br><span class="line"><span class="keyword">self</span>.timer =  [<span class="built_in">NSTimer</span> scheduledTimerWithTimeInterval:<span class="number">1.0</span> target:<span class="keyword">self</span> selector:<span class="keyword">@selector</span>(function:) userInfo:<span class="literal">nil</span> repeats:<span class="literal">YES</span>];  </span><br><span class="line"></span><br><span class="line"><span class="comment">//方式2： 该方式必须显式手动加入到当前循环中去</span></span><br><span class="line"><span class="built_in">NSTimer</span> *timer = [<span class="built_in">NSTimer</span> timerWithTimeInterval:<span class="number">10</span> target:<span class="keyword">self</span> selector:<span class="keyword">@selector</span>(action:) userInfo:<span class="literal">nil</span> repeats:<span class="literal">YES</span>];</span><br><span class="line">[[<span class="built_in">NSRunLoop</span> currentRunLoop] addTimer:_timer forMode:<span class="built_in">NSDefaultRunLoopMode</span>];</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">注意点：</span></span><br><span class="line"><span class="comment">将计数器的repeats设置为YES的时候，self的引用计数会加1。</span></span><br><span class="line"><span class="comment">因此可能会导致self（即viewController）不能release。</span></span><br><span class="line"><span class="comment">所以，必须在viewWillAppear的时候，将计数器timer停止，否则可能会导致内存泄露。</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"><span class="comment">//取消定时器   当调用invalidate方法时, 移除runloop后, iOS系统会解除对NSTimer对象的强引用, 当ViewController销毁时, ViewController和NSTimer就都可以释放了</span></span><br><span class="line">[timer invalidate];   <span class="comment">// 将定时器从运行循环中移除，</span></span><br><span class="line">timer = <span class="literal">nil</span>;    <span class="comment">// 销毁定时器 ---》 这样可以避免控制器不死:必须销毁</span></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">////重点</span></span><br><span class="line"><span class="comment">////要想实现：先停止，然后再某种情况下再次开启运行timer，可以使用下面的方法：</span></span><br><span class="line"><span class="comment">//首先关闭定时器不能使用上面的方法:invalidate是销毁，应该使用下面的方法：</span></span><br><span class="line"><span class="comment">//关闭定时器  </span></span><br><span class="line"><span class="comment">	[NSDate distantFuture];（不可达到的未来的某个时间点）</span></span><br><span class="line"><span class="comment">	[NSDate distantPast];  （不可达到的过去的某个时间点）</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line">[myTimer setFireDate:[<span class="built_in">NSDate</span> distantFuture]];</span><br><span class="line"></span><br><span class="line"><span class="comment">//然后就可以使用下面的方法再此开启这个timer了：</span></span><br><span class="line"><span class="comment">//开启定时器 :使用NSDate设置指定时间 </span></span><br><span class="line">[myTimer setFireDate:[<span class="built_in">NSDate</span> distantPast]];  </span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">//例子：比如，在页面消失的时候关闭定时器，然后等页面再次打开的时候，又开启定时器。</span></span><br><span class="line"><span class="comment">//（主要是为了防止它在后台运行，暂用CPU）可以使用下面的代码实现：</span></span><br><span class="line"><span class="comment">//页面将要进入前台，开启定时器  </span></span><br><span class="line">-(<span class="type">void</span>)viewWillAppear:(<span class="type">BOOL</span>)animated  </span><br><span class="line">&#123;  </span><br><span class="line">    <span class="comment">//开启定时器  </span></span><br><span class="line">    [scrollView.myTimer setFireDate:[<span class="built_in">NSDate</span> distantPast]];  </span><br><span class="line">&#125;  </span><br><span class="line"></span><br><span class="line"><span class="comment">//页面消失，进入后台不显示该页面，关闭定时器  </span></span><br><span class="line">-(<span class="type">void</span>)viewDidDisappear:(<span class="type">BOOL</span>)animated  </span><br><span class="line">&#123;  </span><br><span class="line">    <span class="comment">//关闭定时器  </span></span><br><span class="line">    [scrollView.myTimer setFireDate:[<span class="built_in">NSDate</span> distantFuture]];  </span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<hr>
<h5 id="注意点："><a href="#注意点：" class="headerlink" title="注意点："></a>注意点：</h5><blockquote>
<p>[timer invalidate]是唯一的方法将定时器从循环池中移除<br>NSTimer可以精确到50-100毫秒.<br>NSTimeInterval类：是一个浮点数字，用来定义秒<br>NSTimer不是绝对准确的,而且中间耗时或阻塞错过下一个点,那么下一个点就pass过去了</p>
</blockquote>
<h5 id="NSTimer-暂停-继续"><a href="#NSTimer-暂停-继续" class="headerlink" title="NSTimer 暂停, 继续"></a>NSTimer 暂停, 继续</h5><figure class="highlight plaintext"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">//NSTimer本身没有暂停和继续, 可以使用setFireDate方法设置开始时间来控制.</span><br><span class="line">#import &quot;NSTimer+Addition.h&quot;</span><br><span class="line">@implementation NSTimer (Addition)</span><br><span class="line">- (void)pause</span><br><span class="line">&#123;</span><br><span class="line">    [self setFireDate:[NSDate distantFuture]];</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">- (void)resume</span><br><span class="line">&#123;</span><br><span class="line">    [self setFireDate:[NSDate date]]; //当前时间开始</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">@end</span><br></pre></td></tr></table></figure>

<hr>
<h5 id="底层进阶"><a href="#底层进阶" class="headerlink" title="底层进阶"></a>底层进阶</h5><ul>
<li>NSTimer与runloop</li>
</ul>
<p>上面说到scheduledTimerWithTimeInterval方法时, 有这么一句:schedules it on the current run loop in the default mode</p>
<p>加到runloop这件事就不必再解释了, 而这个default mode应该如何理解呢?</p>
<p>其实我是不想谈runloop的(因为理解不深, 所以怕误导人民群众), 但是这里不得不解释下了</p>
<p>runloop会运行在不同的mode, 简单来说有以下两种mode</p>
<ul>
<li>NSDefaultRunLoopMode, 默认的mode</li>
<li>UITrackingRunLoopMode, 当处理UI滚动操作时的mode</li>
</ul>
<p>所以scheduledTimerWithTimeInterval创建的NSTimer在UI滚动时, 是不会被及时触发的, 因为此时NSTimer被加到了default mode</p>
<p>如果想要runloop运行在UITrackingRunLoopMode时, 仍然及时触发NSTimer那应该怎么办呢?</p>
<p>应该使用timerWithTimeInterval或initWithFireDate, 在创建完NSTimer后, 自己加入到指定的runloop mode</p>
<figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">[[<span class="built_in">NSRunLoop</span> currentRunLoop] addTimer:_timer forMode:<span class="built_in">NSRunLoopCommonModes</span>];</span><br></pre></td></tr></table></figure>

<p>NSRunLoopCommonModes又是什么鬼? 不是说好的只有两种mode么?</p>
<p>是滴, 请注意这里的复数形式modes, 说明它不是一个mode, 它是mode的集合!</p>
<p>通常情况下NSDefaultRunLoopMode和UITrackingRunLoopMode都已经被加入到了common modes集合中, 所以不论runloop运行在哪种mode下, NSTimer都会被及时触发.最后, 我们来做个小测验, 来结束今天的NSTimer讨论吧</p>
<p>测验: 请问下面的NSTimer哪个更准时?</p>
<figure class="highlight objc"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 1</span></span><br><span class="line">[<span class="built_in">NSTimer</span> scheduledTimerWithTimeInterval:TimerInterval</span><br><span class="line">                                 target:<span class="keyword">self</span></span><br><span class="line">                               selector:<span class="keyword">@selector</span>(timerSelector:)</span><br><span class="line">                               userInfo:<span class="literal">nil</span></span><br><span class="line">                                repeats:TimerRepeats];</span><br><span class="line"><span class="comment">// 2</span></span><br><span class="line">[[<span class="built_in">NSRunLoop</span> currentRunLoop] addTimer:_timer</span><br><span class="line">                             forMode:<span class="built_in">NSDefaultRunLoopMode</span>];</span><br><span class="line"><span class="comment">// 3</span></span><br><span class="line">[[<span class="built_in">NSRunLoop</span> currentRunLoop] addTimer:_timer</span><br><span class="line">                             forMode:<span class="built_in">NSRunLoopCommonModes</span>];</span><br></pre></td></tr></table></figure>



</article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="mailto:undefined">Albert Yuan</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="https://yllove.gitee.io/2021/10/12/iOS/ios%E5%AE%9A%E6%97%B6%E5%99%A8%E4%B9%8BNSTimer/">https://yllove.gitee.io/2021/10/12/iOS/ios%E5%AE%9A%E6%97%B6%E5%99%A8%E4%B9%8BNSTimer/</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span class="post-copyright-info">本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" target="_blank">CC BY-NC-SA 4.0</a> 许可协议。转载请注明来自 <a href="https://yllove.gitee.io" target="_blank">Albert Yuan's Blog</a>！</span></div></div><div class="tag_share"><div class="post-meta__tag-list"><a class="post-meta__tags" href="/blog/tags/Objective-c/">Objective-c</a><a 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href="#NSTimer%E5%8F%AB%E5%81%9A%E2%80%9C%E5%AE%9A%E6%97%B6%E5%99%A8%E2%80%9D%EF%BC%8C%E5%AE%83%E7%9A%84%E4%BD%9C%E7%94%A8%E5%A6%82%E4%B8%8B"><span class="toc-text">NSTimer叫做“定时器”，它的作用如下</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%B8%B8%E7%94%A8%E5%B1%9E%E6%80%A7"><span class="toc-text">常用属性</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%95"><span class="toc-text">常用方法</span></a><ol class="toc-child"><li class="toc-item toc-level-5"><a class="toc-link" href="#%E5%9F%BA%E6%9C%AC%E4%BD%BF%E7%94%A8"><span class="toc-text">基本使用</span></a></li><li class="toc-item toc-level-5"><a class="toc-link" href="#%E6%B3%A8%E6%84%8F%E7%82%B9%EF%BC%9A"><span class="toc-text">注意点：</span></a></li><li class="toc-item toc-level-5"><a class="toc-link" href="#NSTimer-%E6%9A%82%E5%81%9C-%E7%BB%A7%E7%BB%AD"><span class="toc-text">NSTimer 暂停, 继续</span></a></li><li class="toc-item toc-level-5"><a 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